docs: def feasible_ratio(self, solutions):
          """counts for each coordinate the number of feasible values in
          ``solutions`` and returns an array of length ``len(solutions[0])``
          with the ratios.
  
          `solutions` is a list or array of repaired ``Solution``
          instances,
  
          """
          raise NotImplementedError('Solution class disappeared')
          count = np.zeros(len(solutions[0]))
          for x in solutions:
              count += x.unrepaired == x
          return count / float(len(solutions))